Process For Making A Shelf-Stable Milk Based Beverage Concentrate

ABSTRACT

A concentrate, system and low-temperature process for preparing a shelf-stable milk concentrate that does not require ultra-high temperature thermal processing for control of the microbiology of the product is disclosed herein. The method preferably incorporates aseptic technology and the enzymatic reduction of lactose to control water activity. The method preferably includes the enzymatic conversion of the lactose in the milk to its component sugars glucose and galactose, which preferably changes the colligative properties of the concentrate, decreases the amount of free water, and reduces the osmolarity.

CROSS REFERENCE TO RELATED APPLICATION

The Present Application claims priority to U.S. Provisional PatentApplication No. 61/075,015, filed on Jun. 24, 2008, which is herebyincorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to processes for making shelf stable milkbeverages.

2. Description of the Related Art

For millennia man has tried unsuccessfully to devise a method forpreserving milk which would retain the nutrients and qualities of freshmilk. Roman soldiers subsisted on rations made from dried milk usingprimitive sun drying techniques. Later technology developed by GailBorden (1858) resulted in sweetened condensed milk which could bepreserved for years using simple concentration methods utilizing wateractivity as the microbiological control point. More modern milkprocessing and packaging technologies combine Ultra-High TemperatureProcessing with aseptic packaging to preserve the shelf-life of milk.The foregoing technologies achieved the preservation aspects but failedto preserve the fresh quality needed for ready to drink products.Sweetened condensed milk is made by concentrating milk 2.5× with addedsucrose to control the water activity (α<0.85). Water activity is ameasure of food dryness. α_(w)=p/p₀, where α_(w) is water activity, p isthe vapor pressure of water in the substance, and p₀ is the vaporpressure of pure water at the same temperature. Water activity as avalue has no dimensions. Pure water has a water activity of 1. Theresulting product is tan in appearance, has a distinct fat off-taste,coarse texture from lactose crystallization and cannot be reconstitutedto a single strength beverage. Similarly, evaporated milk is a 2.1×concentrate which is placed in a can and thermally treated to produce acommercially sterile product (in compliance with 21 CFR113). Theresulting milk is tan in appearance and unacceptable when diluted tosingle strength.

Fluid single-strength milk requires a thermal treatment to controlmicrobial growth, inactivate enzymes and stabilize the milk. ThePasteurized Milk Ordinance requires specific time-temperaturecombinations for the inactivation of infectious pathogens such asCoxiell burnetti, Mycobacterium tuberculosis and Salmonella spp. inrefrigerated milk products. Shelf-stable, UHT milk products require athermal treatment which addresses not only the infectious pathogens butalso the toxin producing, heat-resistant spore-formers like Clostridiumbotulinum or Bacillus cereus. Typical processes for UHT milk requireheating the milk to 286° F. for 6 seconds (or the equivalent process).UHT milk has a pronounced cooked taste and is not well accepted.

UHT/aseptic treatment of milk concentrates has been demonstratedcommercially but is technically very difficult due to problemsassociated with the stability of the concentrated product. Lactoseprecipitation results in a graininess of the product and slowsreconstitution. Hydrolysis of the milk sugar prior to UHT treatmentresults in increased Maillard reaction browning with noticeable changesin the color and flavor of the milk. Hydrolysis prior to UHT alsoresults in decreased shelf-life for the product.

Hydrolysis of lactose prior to processing results in significantincreases in Maillard browning reaction products and produces anunacceptable product. Dosing of lactase enzyme using sterile filtrationsignificantly reduces the browning and extends the life of the product.

The prior art discloses ultra-high pasteurization of milk such asdisclosed in Reaves et al., U.S. Pat. No. 6,887,505, for Ultra-HighTemperature Pasteurized Milk Concentrate, Package, Dispenser And MethodOf Producing Same.

There is a need for a milk concentrate that upon rehydration tastesfresh.

BRIEF SUMMARY OF THE INVENTION

The present invention is preferably a method for preserving milk using aconcentration method that incorporates aseptic technology and theenzymatic reduction of lactose to control water activity. The methodincludes the enzymatic conversion of the lactose in the milk to itscomponent sugars glucose and galactose. This reaction changes thecolligative properties of the concentrate, decreases the amount of freewater, and reduces the osmolarity.

Milk (0.2-3.25% fat) is concentrated using low-temperature, vacuumevaporation to produce a 3.0-4.2× concentrate. As the concentration ofthe milk increases, so does the viscosity. At this point, the additionof lactase enzyme at a rate of 0.01-5 ml per liter results in very rapiddecrease in the lactose concentration resulting in significant changesin the colligative properties of the concentrate. The viscositydecreases and the milks ability to be further concentrated improvesdramatically. Further concentration can be accomplished by furthertreatment in temperature controlled vacuum pans or by the addition ofnon-fat dry milk solids using high shear.

The hydrolysis of lactose requires the incorporation of equal moles ofwater and lactose to yield one mole each of glucose and galactose.Neutral lactase enzyme (2600-4000 units per liter (MaxiLact)) isinjected into the milk concentrate to hydrolyze the lactose sugar intoglucose and galactose. Preferably, a minimum of 70% of the lactose mustbe hydrolyzed and the desired level is in the 98% range. This processreduces water activity by decreasing the amount of water and byincreasing the number of moles of sugar dissolved in the concentrate.Since lactose solubility is about 21.6%, a 4× concentration of milk isthe practical limit of concentration using conventional technology.Further concentration results in graininess, crystallization andviscosity increases. Furthermore, the insoluble lactose must besubtracted from the water activity equation since it is no longerdissolved.

Anhydrous sugar(s) (75/25 w/w) are dissolved in the evaporated milk tobegin reducing the water activity. The mixture is then heated to atemperature sufficient to inactivate vegetative pathogens (160-260° F.)and cooled using vacuum expansion in an aseptic falling film evaporator.The vacuum expansion minimizes the thermal effects of the process on themilk and simultaneously decreases the water concentration by about 1%for every 10 degrees F. of cooling. The product is further cooled toabout 70-120° F. in a tubular heat exchanger and placed in an aseptictank equipped with an agitator. Neutral lactase enzyme (2600-4000 unitsper liter (MaxiLact)) is injected into the milk to hydrolyze the lactosesugar into glucose and galactose. Preferably, a minimum of 70% of thelactose must be hydrolyzed and the desired level is in the 98% range.

The aseptic hydrolysis of lactose accomplishes many purposes. Themajority of humans in the world are lactose intolerant. Hydrolysis ofthe lactose allows them to digest the milk without suffering from gasand bloating. In addition to the nutritional aspects, the hydrolysisreduces the water activity in the product by increasing the molarity ofthe solutes by forming two gram molecular weights of sugars from one.This essentially doubles the osmolarity contribution of the milkcomponent of the formula which reduces the water activity for control ofthe microorganisms. The hydrolysis of the lactose into glucose andgalactose uses one mole of H₂O per mole weight of lactose furtherreducing the water activity.

The thermal process addresses the health and safety aspects of thisproduct by inactivating vegetative pathogens which can survive down to awater activity of 0.85. Toxin forming sporeformers like C. botulinum areunable to grow at a water activity of less than 0.93. The most resistantspore-forming toxin form B. cereus bacteria are unable to grow at awater activity of less than 0.915. Thus, the combination ofconcentration, thermal treatment, enzymatic reduction of water activityand aseptic processing-packaging results in a product which isshelf-stable.

The typical application of this product would be for confectionary use,un-refrigerated distribution of commodity milk, production of whippedtoppings, re-constitution of shakes, malts, smoothies or forre-constitution as a single strength beverage.

The concentrate is not governed by the FDA under 21CFR113 or 21CFR108and is thus exempt from the low-acid canned foods (LACF) regulations.Similarly, condensed milk is not regulated by the Pasteurized MilkOrdinance and is considered by the USDA to be a Class II milk product.

A process for preparing a shelf-stable Pasteurized milk concentratewhich can be reconstituted to a fresh-tasting product is disclosedherein. A low-temperature process for preparing a shelf-stable milkconcentrate that does not require ultra-high temperature thermalprocessing for control of the microbiology of the product is disclosedherein. A method for preserving milk products which minimizes thethermal exposure of the protein fractions to temperatures where they aredenatured which minimizes the thermal damage to the product is disclosedherein. A process for reducing the water activity of the productenzymatically rather than by thermal methods is disclosed herein. Anenzymatic process which changes the colligative properties ofconcentrated milk making it possible to incorporate a higherconcentration of solids is disclosed herein. A method for minimizing thethermal reactions of milk concentration by incorporating dry ingredientsat the end of the process and by chemically increasing the osmolality ofthe product using lactase enzyme is disclosed herein. A method forremoving lactose sugar from milk beverages is disclosed herein. A methodfor preserving a milk concentrate which can be reconstituted anddispensed is disclosed herein. A process for enzymatically removingsugars which promote product “graininess” is disclosed herein. A methodfor preparing a commercially sterile product which uses water activityto prevent the growth of spore-forming pathogens and which utilizesthermal processing to address vegetative spoilage organisms andpathogens is disclosed herein. A method of enzymatically preserving afood product to make it shelf-stable is disclosed herein. A method tocontrol water activity enzymatically is disclosed herein. A method tominimize the browning of shelf-stable lactose reduced milk concentratesis disclosed herein. A method for making a lactose-reduced milkconcentrate having active lactase enzyme is disclosed herein. A methodfor making a lactose-reduced milk concentrate having active lactaseenzyme incorporating aseptic dosing of lactase enzyme into theevaporator effect which maintains the optimum enzyme activity isdisclosed herein.

Having briefly described the present invention, the above and furtherobjects, features and advantages thereof will be recognized by thoseskilled in the pertinent art from the following detailed description ofthe invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a graph of the water activity of concentrated skim milk andlactose reduced skim milk.

FIG. 2 is a block diagram of a system for a thermal processincorporating a microbiological kill step, concentration step, aseptichomogenization, aseptic dosing, an aseptic reaction vessel, a cooler andaseptic packaging.

FIG. 3 is a graph of calculated water activity for concentrated lactosereduced milk with different levels of anhydrous fructose.

FIG. 4 is a block diagram of a system for an aseptic multi-effectevaporator with aseptic filtered lactase enzyme injection, a reactorvessel and aseptic packaging.

FIG. 5 is a graph of temperature (T) and dry matter content (c) of skimmilk as a function of time (t) for a multiple effect evaporatorillustrating the point of introduction of lactase enzyme after effect 4at a temperature of 46 degrees Centigrade.

DETAILED DESCRIPTION OF THE INVENTION

A process for preparing a shelf stable milk concentrate which can bereconstituted into a fresh tasting product is disclosed below.

The product is preferably made from conventional condensed milkformulated with traditional amounts of stabilizers required to maintainthe suspension of milk proteins without precipitation. Anhydrous sugars(sucrose, glucose or fructose) are preferably incorporated (at 0-40%weight) into the pasteurized 4× milk concentrate with agitation andshearing. The temperature during this step is elevated to 40-80° C. toaid in the solublization of the sugars. The formed syrup is preferablyfree of crystals to prevent future crystallization. The warm, sweetenedmilk concentrate is preferably introduced at a pre-determinedtemperature into a pre-sterilized vacuum chamber (500 mbar) to decreasethe temperature and evaporate additional water using technologydeveloped for UHT processing. The vacuum chamber is preferablycontinuously evacuated using an aseptic pump to transfer the materialover to a sterile tank. Further cooling using conventional aseptictubular heat exchangers may be required to reduce the temperature of thesweetened condensed milk to the optimal temperature for lactosehydrolysis. The degree of concentration is preferably regulated by theinitial temperature of the milk product as the milk product isintroduced into the vacuum chamber and the degree of vacuum in thechamber.

A sterile tank is preferably used for a mixing tank to incorporatelactase enzyme into the milk. A solution of lactase enzyme is sterilefiltered using aseptic technology and transferred into the sterile tank.The aseptic tank preferably has aseptic agitation to thoroughly mix anycomponents added to the tank. The enzyme is a neutral lactase enzyme(2,600 to 4,000 lactase enzyme units) at a concentration of between 0.1and 0.0001%. The enzyme acts in the following manner:

Lactose+water→glucose+galactose

The reaction preferably takes one mole of the disaccharide lactose andcreates two moles of the simple sugars glucose and galactose. Thereaction reduces the osmolarity of the condensed milk by doubling themoles of sugar and by using one mole of water for hydrolysis of theα-linkage between the sugar moieties. The resulting product has receiveda thermal treatment adequate to address infectious, vegetative pathogensand has a water activity sufficiently low to prevent the growth of C.botulinum (α<0.93) and B. cereus (α<0.915). The water activity of theproduct is preferably 0.85 or below to address spoilage microbes ofconcern. The product is preferably commercially sterile.

Formulations for some preferred products are provided in Tables One, Twoand Three. Table One is for an unflavored milk product. Table Two is fora vanilla flavored milk product and Table Three is for a chocolateflavored milk product.

TABLE ONE Ingredient Weight % 4X concentrated milk(3.25% fat ss, with70.00% additives) Anhydrous Sugar (sucrose, glucose or 29.99% fructose)Lactase enzyme .01%

Vanilla Milk

TABLE TWO Ingredient Weight % 3.75X concentrated milk (2.0% fat ss,79.754%   with additives) Anhydrous Cane Sugar 20.00%  Vanilla flavor(FONA KS06217wsi) .20% Salt .036%  Lactase enzyme .01%

Chocolate Milk

TABLE THREE Ingredient Weight % 4X Milk (3.25% fat single strength)69.00% Sugar 26.00% Cocoa powder 4.00% Vanilla flavor (anhydrous,ethanol) .99% Lactase enzyme .01%

Mixing

The dry ingredients are preferably completely dissolved in a warmed milkconcentrate along with other ingredients including flavors andstabilizers.

Processing The milk is preferably processed using a system designed forUHT processing system that preheats the milk product to 175° F. usingindirect heating and is capable of injecting live steam into the productto bring it to a sterilizing temperature in the range of 175° F. -310°F. The system is preferably connected to an aseptic tank equipped withagitation and a sterile filtration system. The sterile product ispreferably fed to an aseptic filler downstream of the sterile tank.

The equipment is preferably first brought to a condition of sterility bymeans of raising the temperature of the equipment to a least 250° F. for30 minutes or the equivalent process. The system preferably operates ina water production mode with the hold tube at 280° F. until the milkproduct is introduced into the balance tank. As the milk product entersthe system, the hold tube temperature is preferably reduced so as tomaintain the integrity of the system and provide a minimal process forthe prevention of pathogens in the milk product. The temperature ispreferably brought down to the range of 170-240° F. in the holding tube.At the end of the holding tube, the milk concentrate preferably exitsthrough a pressure reduction valve entering a pre-sterilized vacuumchamber. The concentrate preferably forms a falling film which providesa maximum area for removal of water from the product. The amount ofwater removed is dependent on the initial temperature on introductioninto the chamber and the vacuum level maintained in the chamber.Typically, a vacuum of from7-30 inches of mercury is maintained in thevacuum vessel. The milk product is preferably reduced in moisture by 1%for every 10° F. of temperature decrease.

The final heating of the milk is preferably accomplished with indirectheating such as plate heat exchangers or tubular heat exchangers. Directcoupling of electrical energy with Ohmic heating, direct heating ormicrowave accomplishes a rapid temperature increase without theintroduction of water.

The condensed milk is preferably removed from the vacuum chamber using apositive pump such as a progressive cavity pump made by Moyno. The milkis then preferably conveyed to an aseptic homogenizer where it ishomogenized at 2000/500 psi in two stage aseptic homogenization. Thecondensed milk is preferably conveyed to the final cooler where it iscooled to a temperature of less than 100° F. The milk is preferablyconveyed to the aseptic tank valve cluster for diversion into theaseptic tank.

An aseptic dosing unit, preferably having a filter pore size of 0.2microns, doses 0.1-0.0001% lactase enzyme into the milk concentrate. Theamount of enzyme incorporated is preferably sufficient to quickly reducethe lactose concentration by at least 70% and most preferably by atleast 97%. Other ingredients such as salt (sodium chloride) can besimultaneously injected into the product to reduce the water activityand minimize processing equipment corrosion.

The lactose reduced milk is next packaged in a sterile bag-in-boxcontainer to minimize water incorporation into the product and tominimize the introduction of spoilage microorganisms. The productpreferably has a shelf-life of from 2 months to 12 months depending ofthe storage conditions.

FIG. 1 is graph of the water activity of concentrated skim milk andlactose reduced skim milk showing data that the hydrolysis of lactosecan be used to reduce water activity. The addition of lactase enzyme hasa resultant decrease in water activity. The results clearly demonstratethat water activity can be lowered by enzymatic conversion of lactose toglucose and galactose. The drop in water activity to 0.86 useful forpreservation since bacterial spores can grow down to a water activity of0.915. FIG. 3 is graph of calculated water activity for concentratedlactose reduced milk with different levels of anhydrous fructose. Thegraph shows that a milk concentrate with sucrose added decreases thewater activity (grams/100ml). By changing the sucrose to anhydrousfructose and increasing the lactase enzyme, it is possible to get downto 0.71 preferably using a vacuum process. In an alternative embodiment,additional lactase enzyme is added to get 100% hydrolysis of the milklactose. The formula is preferably underdosed by adding on a volumebasis rather than the moles of lactose basis. As can be seen from thegraph, lactose reduction decreases water activity to 0.87. A vacuumremoval of additional water is preferably used to decrease wateractivity to below 0.85. 4-6% removal corresponds to a 40-60 degreetemperature loss in the vacuum chamber. Lactase enzyme is asepticallyintroduced into the product after cooling. Enzyme hydrolysis provides alowered water activity for a milk concentrate.

Vanilla Milk Formula and Treatment.

A vanilla milk product is made from conventional condensed milk(3.6-4.2× Grassland, Class II Condensed). Lactase enzyme at 0.1-1 ml perliter is immediately added to the concentrate and allowed to react untilthe lactose is 70-99.5% hydrolyzed. After hydrolysis, milk powder (NFDM,Meijers) is added at a level to bring the milk to the desired level ofconcentration. The milk can be 4×-8× concentration as desired. Theproduct is formulated with much lower levels of the traditional amountsof stabilizers required to maintain the suspension of milk proteinswithout precipitation. Anhydrous sugars (sucrose, glucose or fructose)are incorporated (at 0-50% weight (baker's percent)) into thepasteurized 4-8× milk concentrate with agitation and shearing. Thetemperature during this step will need to be elevated to 40-80° C. toaid in the solublization of the sugars and yet not reduce the lactaseenzyme activity. After incorporation of the sugars, the mixture is helduntil the desired water activity is reached (0.9-0.80). Additionalingredients such as stabilizers (gums, CMC or emulsifiers), salt andflavor may be added at this time. The water activity of each ingredientmust be less than 0.85 to minimize adding more water. The formula for afive times concentrate vanilla milk product is set forth in Table Fourand a formula for a six times concentrate vanilla milk product is setforth in Table Five.

TABLE FOUR Ingredient Value Grassland Concentrate 1000 Fructose(anhydrous) 350 NFDM 112 Flavor 25 Salt 2.5

TABLE FIVE Ingredient Value Grassland Concentrate 1000 Fructose(anhydrous) 420 NFDM 208 Flavor 30 Salt 3

The mixture is then preferably thermally treated with a processsufficient to inactivate the vegetative pathogenic organisms. Spoilageorganisms capable of growing in the product under reduced must also beaddressed by the final thermal process. The thermal treatment of thelactose reduced milk concentrate is preferably accomplished either byusing aseptic processing and packaging or by using hot-filling. Theaseptic process uses a presterilized aseptic processing system broughtto the condition of commercial sterility by the application of heat. Assoon as the system is sterilized, the milk product is preferably cooledmaintaining the hold tube temperature and positive pressure. The milkproduct is preferably introduced and is used to push the water out ofthe system. The interface of water and product results in a mixturewhich has a water activity greater than the required limit. Thisinterfacial product must be completely pushed through the system toprevent microbiological growth. As soon as the dissolved solids or wateractivity limits are reached, the milk product is packaged aseptically.

Alternatively, the milk product is heated to Pasteurization temperature(72-125° C.) and then hot-filled into a can, bottle or plasticcontainer. The container is immediately closed and then cooled toambient.

The processing step is preferably used as a final step to reduce thewater content. After delivering the thermal treatment required forcommercial sterility, the hot, lactose reduced milk concentrate isintroduced at a pre-determined temperature into a pre-sterilized vacuumchamber (1-30 inches mercury vacuum) to decrease the temperature andevaporate additional water using aseptic originally technology developedfor UHT processing. The vacuum chamber is preferably continuouslyevacuated using an aseptic pump to transfer the material over to asterile tank. Further cooling using conventional aseptic tubular heatexchangers may be required to reduce the temperature of the sweetenedcondensed milk to the optimal temperature for lactose hydrolysis. Thedegree of concentration is preferably regulated by the initialtemperature of the milk as it is introduced into the vacuum chamber andthe degree of vacuum in the chamber. If additional enzyme is required,the additional enzyme is introduced at this point prior to the aseptictank.

The sterile, aseptic tank is preferably used for a mixing tank toincorporate lactase enzyme into the milk. A solution of lactase enzymeis sterile filtered using aseptic technology and transferred into thesterile tank. The aseptic tank preferably has aseptic agitation tothoroughly mix any components added to the tank. The enzyme is a neutrallactase enzyme (2,600 to 4,000 lactase enzyme units) at a concentrationof between 0.1 and 0.0001%. The enzyme acts in the following manner:

Lactose+water→glucose+galactose

The reaction preferably takes one mole of the disaccharide lactose andcreates two moles of the simple sugars glucose and galactose. Thereaction preferably reduces the osmolarity of the condensed milk bydoubling the moles of sugar and by using one mole of water forhydrolysis of the α-linkage between the sugar moieties. The resultingproduct preferably has received a thermal treatment adequate to addressinfectious, vegetative pathogens and has a water activity sufficientlylow to prevent the growth of C. botulinum (α<0.93) and B. cereus(α<0.915). The water activity of the product is preferably 0.85 or belowto address spoilage microbes of concern. The product is preferablycommercially sterile.

The addition of sugars for sweetening also reduces the water activity.Monosaccharide sugars like fructose, glucose and galactose have twicethe water activity reducing power as disaccharides like glucose orgalactose. Typically, flavored milks have between 5-8% sugar (singlestrength) added to increase the sweetness. Fructose or glucose is/arepreferably used alone or in combination to sweeten and reduce wateractivity. FIG. 3 shows the calculated water activity of lactose reducedmilk (95% reduced) concentrates with varying levels of monosaccharide.

TABLE SIX Ingredient Value Grassland Concentrate 1000 Fructose(anhydrous) 420 NFDM 208 Bakers Chocolate 120 Salt 3

A formula for chocolate milk is set forth in Table Six. The chocolatemilk is made in the same fashion as the vanilla milk with the exceptionof the addition of the baker's chocolate. The chocolate is melted andincorporated into the lactose reduced milk concentrate with high shear.The lactose reduced milk concentrate is preferably then homogenized tofully incorporate the chocolate into a stable emulsion capable ofextended storage. Emulsifiers and stabilizers may be added to enhancestability. The chocolate milk is preferably then thermally treated andpackaged aseptically or hot-filled. Chocolate withstands the hot-fillprocess since color changes are not apparent after hot-filling.

Processing System for Processing Milk with Incorporated Dry Milk Solids.

A processing system 40 for processing a milk product is shown in FIG. 2.The equipment is preferably first brought to a condition of sterility bymeans of raising the temperature of the equipment to a least 250° F. for30 minutes or the equivalent process. The system 40 operates in waterproduction with the hold tube at 280° F. until a milk product isintroduced into a balance tank 51. As the milk product enters the system40, a temperature of a hold tube 54 is reduced so as to maintain theintegrity of the system 40 and provide a minimal process for theprevention of pathogens in the milk product. The components of thesystem 40 are in flow communication through aseptic tubing 50. Thetemperature can be brought down to the range of 170-240° F. in theholding tube 54. At the end of the hold tube 54, the milk product exitsthrough a pressure reduction valve entering a pre-sterilized vacuumvessel 55. The milk product preferably forms a falling film whichprovides maximum area for removal of water from the milk product. Theamount of water removed is dependent on the initial temperature onintroduction into the chamber and the vacuum level maintained in thechamber. Typically, a vacuum of from 7-30″ of mercury is maintained inthe vacuum vessel 55. The milk product is preferably reduced in moistureby 1% for every 10° F. of temperature decrease. The final heating of themilk is accomplished with indirect heating such as plate heat exchangersor tubular heat exchangers. Although steam injection (provided by anoptional steam injector 53) is commonly used for milk products,preferably in this system 40 a steam injector is not utilized to avoidthe introduction of additional water which must be subsequently removed.Alternatively, direct coupling of electrical energy with Ohmic heating,direct heating or microwave accomplishes a rapid temperature increasewithout the introduction of additional water into the milk product.

A condensed milk is removed from the vacuum vessel 55, preferably usinga centrifugal or positive pump such as a progressive cavity pump made byMoyno. The condensed milk is conveyed to an aseptic homogenizer 56 wherethe condensed milk is homogenized, preferably at 2000/500 psi in a twostage aseptic homogenization. The homogenized condensed milk ispreferably conveyed to a cooler where the homogenized condensed milk ispreferably cooled to a temperature of less than 100° F. The cooled,homogenized condensed milk is preferably conveyed to an aseptic tankvalve cluster for diversion into an aseptic reactor tank 59.

An aseptic dosing unit 58, preferably having a filter pore size of 0.2microns, doses 0.1-0.0001% lactase enzyme from a balance tank 57 intothe aseptic reactor tank 59 having the cooled, homogenized condensedmilk to create a lactose reduced milk product. The amount of enzymeincorporated is preferably sufficient to quickly reduce the lactoseconcentration by at least 70% and most preferably by at least 97%. Otheringredients such as salt (sodium chloride) are simultaneously injectedinto the aseptic reactor tank 59 to preferably reduce the water activityand minimize processing equipment corrosion.

The lactose reduced milk product is preferably next cooled at a cooler60, and packaged, using an aseptic filling machine 61, in a sterilebag-in-box container 65 to minimize water incorporation into the productand to minimize the introduction of spoilage microorganisms. The productpreferably has a shelf-life of from 2 months to 12 months depending onthe storage conditions. Since the microbiology is water activitycontrolled, there is no need of micro testing to assure the commercialsterility of the product and thus the final product can be immediatelyreleased for distribution.

Processing System for Making a High-Solids, Liquid, Lactose Reduced,Milk Concentrate.

Multi-effect effect evaporators are preferably used to remove water frommilk to make milk concentrates. A typical evaporator uses 6-effects forsequential water removal. One such multi-effect evaporator is an ANHYDROEvaporation System available from Anhydro A/S of Copenhagen, Denmark(see www.anhydro.com). Each successive step operates at a lower pressureand subsequently at a lower temperature as well.

FIG. 4 is a block diagram of a system 100 for an aseptic multi-effectevaporator with aseptic filtered lactase enzyme injection, a reactorvessel and aseptic packaging.

At the first effect 103 a, raw milk in a single strength balance tank101 is heated with an indirect heater 102 to 100° C. for 0.0001-5minutes to inactivate target microorganisms and inactivate enzymes.After the hold time, it is injected into the first effect where water isflashed off rapidly reducing the temperature as the moisture is removed.The typical temperature profile for the milk undergoing the evaporationprocess is illustrated FIG. 5. As the milk resides in the pan of thefirst effect, additional heat is added to provide the energy toevaporate the water. The temperature of the first effect is about 70° C.The solids content increases from 10% to 13% in the first effect.

At the second effect 103 b, the milk is pumped from the first effectinto the second effect which is maintained at a slightly lower pressure.The pressure in the second effect also dictates the temperature which isusually about 5° C. lower than the first effect. The milk solidsincrease from 13 to 18% as water is removed.

At the third effect 103 c, the milk is pumped from the second effectinto the third effect which is maintained at a slightly lowertemperature about 3° C. lower than the previous effect. The solidscontent increases from 18% to 27%.

At the third effect 103 d, the milk is pumped from third effect into thefourth effect which is maintained at a slightly lower pressure about 2°C. than effect three. Effect 4 is at 60° C. This temperature is a legalpasteurization temperature but also can reduce the activity of lactaseenzyme. The solids content increase from 28% to 34% in this effect.

At the fifth effect 107 a, the milk from effect 4 is pumped into thevacuum vessel of effect 5 at a temperature of 60° C. At this point,while the milk is at 60° C., the lactase enzyme is introduced into themilk. As the enzyme is added, it is simultaneously flashed into fiftheffect 107 a reducing the temperature to 48° C. Lactase enzyme has itshighest activity at 47° C. and thus this is the optimum location forintroduction of the enzyme. The security of the dosing valve ismaintained by the temperature and the activity of the enzyme is optimal.As the enzyme resides in the pan of fifth effect 107 a, the enzymerapidly hydrolyzes the lactose and changes the colligative propertiesmaking it easier to handle by reducing viscosity. The solids content ofthe concentrate increase from 34% to 42% as water is evaporated.Additional water is used from the hydrolysis reaction further increasingthe solids content.

At the sixth effect 107 b, the milk from fifth effect 107 a is pumpedinto the final vacuum vessel of the sixth effect 107 b which is at atemperature of 43° C. Additional water is removed in this sectionincreasing the solids concentration from 42% to 50%. Enzyme added in thefifth effect 107 a remains active in this effect and all subsequentprocess. The milk from sixth effect 107 b is a 1+4 concentrate or a 5×milk. Further concentration can be achieved on the same equipment byincreasing the residence time and increasing temperatures to accomplisha higher reduction. The product is then pumped to aseptic tank 108 andstored at 80° F. Then the product is preferably pumped to asepticfilling machine 109 for packaging into an aspectic container 120.

Table Seven set forth the contents of an example pre and post hydrolysisto a 7.2 times concentration.

TABLE SEVEN Post-hydrolyzation and Proximates Pre-hydrolyzation 7.2 Xconc. Water (g) 90.84 34.08 Energy (kcal) 34 Energy (kj) 143 Protein (g)3.37 3.37 Total lipid (fat) (g) 0.08 0.08 Ash (g) 0.75 0.75 Glucose (g)0 2.4175 Fructose (g) 0 Lactose (g) 5.09 0.2545 Galactose (g) 0 2.4175Water activity 0.99 0.85

From the foregoing it is believed that those skilled in the pertinentart will recognize the meritorious advancement of this invention andwill readily understand that while the present invention has beendescribed in association with a preferred embodiment thereof, and otherembodiments illustrated in the accompanying drawings, numerous changesmodification and substitutions of equivalents may be made thereinwithout departing from the spirit and scope of this invention which isintended to be unlimited by the foregoing except as may appear in thefollowing appended claim. Therefore, the embodiments of the invention inwhich an exclusive property or privilege is claimed are defined in thefollowing appended claims.

1. A method for preparing a shelf-stable milk concentrate, the methodcomprising: concentrating milk using low temperature, vacuum evaporationto produce a milk concentrate; adding a lactase enzyme and water to themilk concentrate to hydrolyze the milk concentrate into a concentrate ofglucose and galactose; and dissolving anhydrous sugar into theconcentrate of glucose and galactose to form a shelf-stable milkconcentrate with minimal water activity.
 2. A method for preparing ashelf-stable milk concentrate, the method comprising: adding a lactaseenzyme and water to a milk concentrate to hydrolyze the milk concentrateinto a hydrolyzed milk concentrate comprising glucose and galactose, thehydrolyzed milk concentrate having a minimal water activity.
 3. Themethod according to claim wherein a minimal water activity is less than0.85.
 4. The method according to claim 2 further comprising: adding amilk powder to the hydrolyzed milk concentrate to create a second milkconcentrate having 4 times to 8 times concentration; adding anhydroussugar to the second milk concentrate with agitation and shearing tocreate a first milk mixture, the anhydrous sugar added in an amountranging from 1 to 50 weight percent of the first milk mixture; heatingthe first milk mixture to a temperature ranging from 40° C. to 80° C.;holding the first milk mixture until a water activity of the first milkmixture ranges from 0.8 to 0.9; adding at least one additionalingredient to the held first milk mixture to create a second milkmixture; thermally treating the second milk mixture to create a finishedmilk concentrate; and packaging the finished milk concentrate.
 5. Themethod according to claim 4 wherein the additional ingredient comprisesat least one of stabilizers, salt and flavoring.
 6. The method accordingto claim 4 wherein thermally treating the second milk mixture comprisesheating the second milk mixture to a Pasteurization temperature rangingfrom 72° C. to 125° C.
 7. The method according to claim 4 wherein theadditional ingredient comprises at least one of stabilizers, salt andchocolate.
 8. The method according to claim 2 further comprising:introducing a milk product into a balance tank; heating the milk productin a holding tube at a temperature ranging from 170° F. to 240° F. tocreate a heated milk product; introducing the heated milk product into apre-sterilized vacuum chamber as a falling film to remove water from theheated milk product to create a condensed milk product; and homogenizingthe condensed milk product in an aseptic homogenizer to create the milkconcentrate.
 9. The method according to claim 2 further comprising:introducing a raw milk product into a balance tank; heating the raw milkproduct in a preheater to create a preheated milk product; injecting thepreheated milk product into a first effect wherein the preheated milkproduct is heated at a temperature of about 70° C. to evaporate waterand increase a solids content of the preheated milk product to create afirst effect milk product with a solids concentration of from 10% to13%; injecting the first effect milk product into a second effectwherein the first effect milk product is heated at a temperature ofabout 65° C. to evaporate water and increase a solids content of thefirst effect milk product to create a second effect milk product with asolids concentration of from 13% to 18%; injecting the second effectmilk product into a third effect wherein the second effect milk productis heated at a temperature of about 62° C. to evaporate water andincrease a solids content of the second effect milk product to create athird effect milk product with a solids concentration of from 18% to27%; injecting the third effect milk product into a fourth effectwherein the third effect milk product is heated at a temperature ofabout 60° C. to evaporate water and increase a solids content of thethird effect milk product to create the milk concentrate with a solidsconcentration of from 28% to 34%; injecting the milk concentrate into afifth effect along with the a lactase enzyme, wherein the fifth effectis heated at a temperature of about 48° C. to evaporate water andincrease a solids content to create hydrolyzed milk concentrate with asolid concentration of from 34% to 42%; injecting the hydrolyzed milkconcentrate into a sixth effect wherein the hydrolyzed milk concentrateis heated at a temperature of about 43° C. to evaporate water andincrease a solids content of hydrolyzed milk concentrate to create afinal hydrolyzed milk concentrate with a solids concentration of from42% to 50%; holding the final hydrolyzed milk concentrate in an aseptictank at a temperature of about 80° F.; and packaging the finalhydrolyzed milk concentrate in an aseptic container using an asepticfilling machine.
 10. The method according to claim 9 wherein the rawmilk product is heated to a temperature of 100° C. for a time periodranging from 1 second to five minutes to inactive a plurality ofmicroorganisms and a plurality of enzymes.
 11. The method according toclaim 2 further comprising reconstituting the hydrolyzed milkconcentrate into a fresh-tasting product.
 12. The method according toclaim 2 further comprising minimizing a plurality of thermal reactionsof the hydrolyzed milk concentrate by incorporating a plurality of dryingredients at an end of the method and by chemically increasing theosmolality of the hydrolyzed milk concentrate using the lactase enzyme.13. A system for preparing a shelf-stable milk concentrate, the systemcomprising: a source of a milk product; means for concentrating the milkproduct using low temperature, vacuum evaporation to produce a milkconcentrate; and means for adding a lactase enzyme and water to the milkconcentrate to hydrolyze the milk concentrate into a hydrolyzed milkconcentrate comprising glucose and galactose.
 14. The system accordingto claim 13 further comprising means for dissolving anhydrous sugar intothe hydrolyzed milk concentrate to form a shelf-stable milk concentratewith minimal water activity.
 15. The system according to claim 13wherein the means for concentrating the milk product comprises aplurality of effects.
 16. The system according to claim 13 wherein themeans for concentrating the milk product comprises an aseptic vacuumcooling vessel.
 17. The system according to claim 16 wherein the meansfor concentrating the milk product further comprises an aseptichomogenizer.
 18. The system according to claim 14 further comprisingmeans for aseptically packaging the shelf-stable milk concentrate. 19.The system according to claim 14 wherein the shelf-stable milkconcentrate has a water activity value lower than 0.85.
 20. The systemaccording to claim 13 wherein the hydrolyzed milk concentrate is from70% to 99.5% hydrolyzed.